U.S. patent number 5,933,004 [Application Number 08/862,844] was granted by the patent office on 1999-08-03 for low profile modular revenue meter.
This patent grant is currently assigned to Siemens Power Transmission & Distribution, LLC. Invention is credited to Thomas P. Houck, Philip L. Jackson, John T. Voisine.
United States Patent |
5,933,004 |
Jackson , et al. |
August 3, 1999 |
Low profile modular revenue meter
Abstract
An electronic utility meter includes a sensor module and a
removable measurement module. The sensor module connects to the
electrical system of a facility and includes voltage and current
sensors. The voltage and current sensors is operable to receive
voltage and current signals from the electrical system and generate
measurement signals therefrom. The sensor module further includes
an electrically safe interface. The removable measurement module
includes a measurement circuit operable to receive measurement
signals and generate energy consumption data therefrom. The
measurement module also includes a device for communicating
information relating to the energy consumption data. The
electrically safe interface of the sensor module operably connects
the voltage and current sensors to the measurement circuit, and
further prevents physical contact of a human operator with the
received voltage and current signals from the electrical system
when the measurement module is removed from the sensor circuit.
Inventors: |
Jackson; Philip L. (West
Lafayette, IN), Houck; Thomas P. (West Lafayette, IN),
Voisine; John T. (Lafayette, IN) |
Assignee: |
Siemens Power Transmission &
Distribution, LLC (Wendell, NC)
|
Family
ID: |
26690846 |
Appl.
No.: |
08/862,844 |
Filed: |
May 23, 1997 |
Current U.S.
Class: |
324/142; 324/110;
324/156 |
Current CPC
Class: |
G01R
22/065 (20130101) |
Current International
Class: |
G01R
11/00 (20060101); G01R 11/04 (20060101); G01R
011/32 () |
Field of
Search: |
;324/13R,107,110,127,141,142,156
;361/641,657,659,664,666,668,669,671,672 ;702/60,61,62,64,65 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Do; Diep N.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a continuation-in-part of U.S. patent application Ser. No.
60/018,201, filed May 23, 1996
Claims
What is claimed:
1. An electronic utility meter comprising:
a) a sensor module for connecting to the electrical system of a
facility, said sensor module having an interior including voltage
and current sensing means, said voltage and current sensing means
operable to receive voltage and current signals from the electrical
system and generate measurement signals therefrom, the sensor
module further having first interconnecting means;
b) a measurement module including a measurement circuit operable to
receive measurement signals and generate energy consumption data
therefrom, said measurement module including means for
communicating information relating to the energy consumption data,
said measurement module further containing second interconnecting
means;
wherein said first interconnecting means and said second
interconnecting means cooperate to connect the measurement circuit
to the voltage and current sensing means, and wherein said first
interconnecting means includes means for preventing physical
contact of a human operator with at least a part of the voltage and
current sensing means that carries potentially hazardous electrical
signal levels.
2. The electronic utility meter of claim 1 wherein the means for
preventing physical contact comprises a top plate that
substantially covers the interior of the sensor module.
3. The electronic utility meter of claim 2 wherein the second
interconnecting means includes a plurality of plugs and the first
interconnecting means includes a plurality of sockets for receiving
said plurality of plugs, and wherein the top plate includes a
plurality of openings situated in a coordinated relationship with
the plurality of sockets to allow the plurality of plugs to be
received in the plurality of sockets through the plurality of
openings.
4. The electronic utility meter of claim 3 wherein the plurality of
openings each have a first dimension and a second dimension, the
first dimension having at least the same size as the second
dimension, and wherein the second dimension is less than 1/8 inch,
thereby preventing substantial access of a human operator through
the openings.
5. The electronic utility meter of claim 2 wherein the top plate
includes a plurality of openings situated to allow the first
interconnecting means and said second interconnecting means to
cooperate to connect the measurement circuit to the voltage and
current sensing means.
6. The electronic utility meter of claim 5 wherein the plurality of
openings each have a first dimension and a second dimension, the
first dimension having at least the same size as the second
dimension, and wherein the second dimension is less than 1/8 inch,
thereby preventing substantial access of a human operator through
the openings.
7. The electronic utility meter of claim 1 wherein the sensor
module is operable to be received by a cooperating meter box, the
meter box having a housing and a meter box cover, and the sensor
module is further operable to receive a meter box cover, such that
the meter box cover and said means for preventing physical contact
cooperate to prevent the physical contact to at least a portion of
the voltage and current sensing means.
8. The electronic utility meter of claim 1 wherein the voltage and
current sensing means further comprises a pre-calibrated voltage
and sensing means having a signal response, said signal response
having a tolerance no greater than a tolerance of an energy
measurement accuracy of the electronic utility meter.
9. The electronic utility meter of claim 1 wherein the voltage and
current sensing means includes:
a plurality of current coils each having a first and second end,
said first and second end each terminating in a blade; and
a plurality of current transformers in a current sensing
relationship to the current coils, wherein said current
transformers are electrically connected to the first
interconnecting means.
10. The electronic utility meter of claim 9 wherein the sensor
module and the measurement module each have an axial dimension, a
radial dimension, and wherein the plurality of current transformers
each comprise a toroid having a substantially circular shape, and
wherein the axis defined by each toroid is parallel to the axial
dimension of the sensor and measurement module.
11. An electronic utility meter comprising:
a) a sensor module for connecting to the electrical system of a
facility, said sensor module including voltage and current sensing
means, said voltage and current sensing means operable to receive
voltage and current signals from the electrical system and generate
measurement signals therefrom, said sensor module further
comprising an electrically safe interface;
b) a removable measurement module including a measurement circuit
operable to receive measurement signals and generate energy
consumption data therefrom, said measurement module including a
means for communicating information relating to the energy
consumption data;
wherein said electrically safe interface operably connects the
voltage and current sensing means to the measurement circuit, said
electrically safe interface further preventing physical contact of
a human operator with the received voltage and current signals from
the electrical system when the measurement module is removed from
the sensor circuit.
12. The electronic utility meter of claim 11 wherein the
electrically safe interface includes a top plate that is integral
with and substantially covers the interior of the sensor
module.
13. The electronic utility meter of claim 11 wherein the
measurement module includes a plurality of plugs connected to the
measurement circuit and the electrically safe interface includes a
plurality of sockets for receiving said plurality of plugs, said
plurality of plugs integral with the sensor housing.
14. The electronic utility meter of claim 13 wherein the
electrically safe interface includes a top plate that is integral
with and substantially covers the interior of the sensor module,
and wherein the top plate includes a plurality of openings situated
in a coordinated relationship with the plurality of sockets to
allow the plurality of plugs to be received in the plurality of
sockets through the plurality of openings.
15. The electronic utility meter of claim 14 wherein the plurality
of openings each have a first dimension and a second dimension, the
first dimension having at least the same size as the second
dimension, and wherein the second dimension is less than 1/8 inch,
thereby preventing substantial access of a human operator through
the openings.
16. The electronic utility meter of claim 11 wherein the sensor
module is operable to be received by a cooperating meter box, the
meter box having a housing and a meter box cover, and the sensor
module is further operable to receive a meter box cover, such that
the meter box cover and the electrically safe interface cooperate
to prevent the physical contact of a human operator with the
voltage and current signals received from the electrical
system.
17. The electronic utility meter of claim 11 wherein the voltage
and current sensing means includes:
a plurality of current coils each having a first and second end,
said first and second end each terminating in a blade; and
a plurality of current transformers in a current sensing
relationship to the current coils.
18. The electronic utility meter of claim 11 wherein the voltage
and current sensing means further comprises a pre-calibrated
voltage and sensing means having a signal response, said signal
response having a tolerance no greater than a tolerance of an
energy measurement accuracy of the electronic utility meter.
19. The electronic utility meter of claim 17 wherein the sensor
module and the measurement module each have an axial dimension, a
radial dimension, and wherein the plurality of current transformers
each comprise a toroid having a substantially circular shape, and
wherein the axis defined by each toroid is parallel to the axial
dimension of the sensor and measurement module.
20. A method of servicing an electronic utility meter, said utility
meter operably connected to an electrical system of a facility for
the purposes of measuring a power consumption of the facility, said
method comprising:
a) removing a measurement module of the electronic utility meter
from a sensor module of the electronic utility meter while the
sensor module is electrically connected to the electrical system
and while said electrical system is providing power to the
facility, said sensor module including voltage and current sensing
means, said voltage and current sensing means operable to receive
voltage and current signals from the electrical system and generate
measurement signals therefrom, wherein said measurement module
includes a measurement circuit operable to receive measurement
signals and generate energy consumption data therefrom, said
measurement module including a display for displaying information
relating to the energy consumption data, said measurement module
having a first level of performance; and
b) replacing the measurement module with a replacement module
having a second level of performance.
21. The method of claim 20 further comprising a step c), performed
prior to step b), of performing an operation on the measurement
module having a first level of performance to create the
replacement module having a second level of performance.
22. The method of claim 21 wherein step c) further comprises
performing an operation including upgrading the measurement circuit
to create the replacement module having a second level of
performance.
23. The method of claim 21 wherein the measurement module includes
at least one inoperative component and step c) further comprises
performing an operation including replacing the at least one
inoperative component to create the replacement module having a
second level of performance.
24. The method of claim 20 wherein the measurement module having a
first level of performance comprises a first measurement module and
the replacement measurement module comprises a second measurement
module and step b) further comprises replacing the first
measurement module with the second measurement module.
25. An electronic utility meter comprising:
a) a sensor module for connecting to the electrical system of a
facility, said sensor module having an interior including voltage
and current sensing means, said voltage and current sensing means
operable to receive voltage and current signals from the electrical
system and generate measurement signals therefrom, the sensor
module including an interface;
b) a removable measurement module including a measurement circuit
operable to receive measurement signals and generate energy
consumption data therefrom, said measurement module including a
display for displaying information relating to the energy
consumption data;
wherein the interface operably connects the measurement circuit to
the voltage and current sensing means, said interface having a
depression defined in part by the configuration of the voltage and
current sensing means, said depression forming a recess space
exterior the sensor module for receiving at least a portion of the
measurement module.
26. The revenue meter of claim 25 wherein the interface further
comprises an electrically safe interface, said electrically safe
interface operable to prevent physical contact of a human operator
with the interior of the sensor module when the measurement module
is removed from the sensor circuit.
27. The electronic utility meter of claim 25 wherein the voltage
and current sensing means includes:
a plurality of current coils each having a first and second end,
said first and second end each terminating in a blade; and
a plurality of current transformers in a current sensing
relationship to the current coils.
28. The electronic utility meter of claim 27 wherein the sensor
module and the measurement module each have an axial dimension, a
radial dimension, and wherein the plurality of current transformers
each comprise a toroid having a substantially circular shape, and
wherein the axis defined by each toroid is parallel to the axial
dimension of the sensor and measurement module.
29. The electronic utility meter of claim 26 wherein the sensor
module is operable to be received into an interior of a meter box,
the meter box having a housing and a meter box cover, and the
sensor module is further operable to receive a meter box cover,
such that the meter box cover and said electrically safe interface
cooperate to prevent physical contact by a human operator with the
interior of the meter box.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of metering
devices, and in particular, to electrical utility revenue
meters.
Electrical utility revenue meters, or simply revenue meters, are
devices that, among other things, measure electrical energy
consumed by a residence, factory, commercial establishment or other
such facility. Electrical utilities rely on revenue meters for many
purposes, including billing customers and tracking demand for
electrical power. A common form of revenue meter comprises an
inductive drive that rotates a spinning disk at an angular velocity
proportional to the amount of power being consumed. The spinning
disk drives mechanical counters that provided an indication of
power consumed over time.
Over recent years, electronic meters have been developed that are
replacing the spinning disk meter design in several applications.
Electronic meters use electronic circuits to measure, quantify and
display energy consumption information. In general, electronic
meters may be divided into two portions, a sensor portion and a
measurement portion. The sensor portion includes sensor devices
that are connected to the electrical system of a facility, and more
particularly, to the power lines. The sensor devices generate
signals that are indicative of the voltage and current in the power
lines. In general, the sensor portion of a revenue meter operates
with the high voltages and currents that are present on the power
lines.
The measurement portion of an electronic meter uses the signals
generated by the sensor portion to determine watt-hours, VA, VAR
and other information that quantifies the power consumed by the
facility. The measurement portion typically also includes a display
for displaying the power consumption information. In contrast to
the sensor portion, the measurement circuit works with reduced or
attenuated voltage and current signals that are compatible with
electronic devices, and in particular, digital electronic
devices.
Occasionally, revenue meters can malfunction or suffer damage
through external forces and require repair or replacement. Repair
or replacement of many commonly-used revenue meters presently
require an interruption in the electrical power to the facility
being metered. In general, power service interruptions are
extremely undesirable from the electrical utilities' perspective
because they reduce customer satisfaction. Accordingly, there
exists a need for a revenue meter that may be repaired or replaced
without interrupting power service to the facility being
metered.
Another problem that has arisen due to the advent of electronic
meters pertains to service upgrades. In general, electronic meters
offer a wide variety of features that are facilitated by digital
electronics. These features may include power demand monitoring,
communications, and power line and meter diagnostics. Because these
feature are facilitated by the digital circuitry in the measurement
portion of the meter, the services or functions available in an
electronic-type revenue meter may be altered by replacing digital
circuit components in the measurement portion of the meter.
For example, consider a utility that installs several electronic
meters without power demand monitoring because it is deemed
unnecessary at the time of installation. A year later that utility
may determine that it would be desirable to have the power demand
monitoring capability in those meter installations. The installed
electronic meters may, in theory, be upgraded to provide that
capability typically by replacing portions of the electronic
portion. The sensor portion components would not need to be
replaced.
As a practical matter, however, it is often more convenient to
replace the entire meter rather than the individual digital circuit
components. Accordingly, enhancement of the capabilities of the
metering often requires replacement of the entire meter.
Replacement of the entire meter, however, undesirably creates waste
by forcing the replacement of relatively costly, and perfectly
operable, sensor components.
A meter introduced by Asea Bover & Brown ("ABB") addresses this
concern by providing a modular meter that includes a sensor portion
and a removable measurement portion. The measurement portion may be
removed from the sensor module and replaced with another
measurement portion having enhanced functionality. The ABB meter,
however, has significant drawbacks. For example, the measurement
portion of the ABB meter can not be replaced while the sensor
portion is connected to an electrical system of a facility because
removal of the measurement portion would expose extremely dangerous
voltages and currents to a human operator or technician. Thus,
although the modular design allows for upgrades, the power to the
facility must nevertheless be interrupted to perform such upgrades
for safety purposes.
A further problem with the ABB meter arises from its bulkiness. The
sensor portion of the ABB meter is enclosed in housing and the
measurement portion is enclosed in another housing. Both housings
include large areas of unused space that increase the bulkiness of
the meter. The bulkiness undesirably increases costs in shipping
and storing of the meters both as assembled or in their modular
components.
There exists a need, therefore, for a modular meter having modular
components that may be removed or replaced without interruption to
the electrical power service to the facility to which the meter is
connected. There is also a need for a revenue meter having reduced
bulkiness.
SUMMARY OF THE INVENTION
The present invention overcomes the above stated needs, as well as
others, by providing a modular safety meter comprising a sensor
module, a measurement module, and an electrically safe interface.
The electrically safe interface allows the measurement module to be
removed from sensor module without exposing dangerous electrical
voltages. The present invention further provides a novel
configuration of circuit components that reduce the thickness or
bulkiness of the meter.
An exemplary embodiment of the present invention is an electronic
utility meter comprising a sensor module and a removable
measurement module. The sensor module connects to the electrical
system of a facility, said sensor module including voltage and
current sensing means. The voltage and current sensing means are
operable to receive voltage and current signals from the electrical
system and generate measurement signals therefrom. The sensor
module further includes first interconnecting means, which includes
an electrically safe interface.
The removable measurement module includes a measurement circuit
operable to receive measurement signals and generate energy
consumption data therefrom. The measurement module also includes a
means for communicating information relating to the energy
consumption data. The measurement module further includes second
interconnecting means. The first interconnecting means and the
second interconnecting means cooperate to connect the measurement
circuit to the voltage and current sensing means, wherein said
first interconnecting means includes means for preventing physical
contact of a human operator with the voltage and current sensing
means.
The above discussed features and advantages, as well as others, may
readily be ascertained by those of ordinary skill in the art by
reference to the following detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an exploded view of an exemplary embodiment of a
revenue meter according to the present invention;
FIG. 1a shows an optional bottom structure for the meter of FIG.
1;
FIG. 2 shows an installation configuration that includes the meter
from FIG. 1, and a meter box comprising a housing and a cover;
FIG. 3 shows a schematic circuit diagram of the sensor module of
the exemplary embodiment of the revenue meter of FIG. 1;
FIG. 4 shows an exemplary measurement circuit and associated
display for use on the printed circuit board in the measurement
module of FIG. 1; and
FIG. 5 shows a side view cutaway of the exemplary embodiment of the
revenue meter of FIG. 1.
DETAILED DESCRIPTION
FIG. 1 shows an exploded view of an exemplary revenue meter 10
according to the present invention. The revenue meter 10 includes a
sensor module 12 and a measurement module 14. The revenue meter 10
is constructed as described below such that the measurement module
14 is removable from the sensor module 12. The exemplary revenue
meter 10 is a type of meter known in the revenue metering industry
as a 12S meter form. The meter form relates to the application of
the meter installation, for example, whether it is single phase or
polyphase. In any event, it will be noted that the present
invention is not limited to applications involving 12S meter forms,
but may readily be incorporated into 2S, 8S/9S and other well known
meter forms by those of ordinary skill in the art.
The sensor module 12 includes voltage and current sensing means,
which according to the exemplary embodiment described herein,
includes first and second current transformers 16a and 16b,
respectively, first and second current coils 18a and 18b,
respectively, and one or more neutral blades 20. The first current
coil 18a includes first and second ends defining first and second
current blades 22a and 24a, respectively, to be received by the
jaws of a compatible meter socket. (See FIG. 2) The second current
coil 18b likewise includes first and second ends defining first and
second current blades 22b and 24b, respectively, to be received by
the jaws of compatible meter socket. (See FIG. 2)
The first and second current transformers 16a and 16b,
respectively, are preferably toroidal transformers having a
substantially circular shape defined by a circular core. In the
present embodiment, the first current transformer 16a has a turns
ratio of N1 and the second current transformer has a turns ratio of
N2. Using such toroidal current transformers, the first current
coil 18a, when assembled, passes through the interior of the toroid
of the first current transformer 16a. Preferably, the current
transformer 16a is arranged such that the axial dimension of the
current transformer 16a is substantially parallel to the axial
dimension of the sensor module 12. In other words, the current
transformer 16a is horizontally-disposed within the sensor module
12. The second current transformer 16b and the second current coil
18b are preferably arranged in a similar manner within the sensor
module 12. Accordingly, the second current transformer 16b is also
horizontally disposed within the sensor module 12. The use of
horizontally disposed toroidal current transformers reduces the
thickness and thus reduces the overall bulk of the meter 10.
The sensor module 12 further includes an electrically safe
interface 26. The electrically safe interface 26 comprises a first
interconnecting means for connecting to the measurement module 14.
The electrically safe interface 26 also includes means for
preventing physical contact of a human operator with potentially
hazardous electrical signals present on at least a portion of the
voltage and current sensing means 15. Signal levels which are
considered potentially hazardous are well-known. Different levels
of potential hazard also exist. For example, signals capable of
generating shock currents exceeding 70 milliamperes are possibile
burn hazards, while signals generating shock currents on the order
of 300 milliamperes may constitute life threatening hazards.
Furthermore, signals generating shock currents as low as 0.5 to 5
milliamperes are known to cause an involuntary startle
reaction.
In revenue meters, including the meter 10 of the present invention,
at least some of the sensor devices carry such potentially
hazardous electrical signals. Specifically, any portion of the
sensor module 12 that is electrically connected to the voltage and
current signals from the power line is a life threatening hazard
and must be isolated from human contact by the electrically safe
interface 26. In the present embodiment, the current coils 18a and
18b are directly connected to the facility power line and therefore
must be isolated. By contrast, the current transformers 16a and
16b, do not necessarily carry life threatening currents because, as
discussed later, the current transformers 16a and 16b are not
directly coupled to the facility power lines. Accordingly,
depending on the highest level of expected current flowing through
the current transformers 16a and 16b, the current transformers 16a
and 16b may or may not carry potentially hazardous electrical
signals. In any event, however, the electrically safe interface 26
preferably prevents human contact with the entire voltage and
current density means 15 as a safety measure.
In the present embodiment, the means for preventing physical
contact includes a top plate 28, and a plurality of sockets 30a,
30b, 30c, 30d, 30e, 30f and 30g. Each of the sockets 30a through
30g defines an opening in the top plate 28. Other than the openings
defined by the sockets 30a through 30g, the top plate 28 preferably
forms a complete barrier or wall from the measurement module 14 to
the voltage and current sensing means 15.
Alternatively, at a minimum, the top plate 28 operates to prevent
human contact with the portions of the voltage and current sensing
means 15 that directly contact the power lines of the facility, and
in Particular, the current coils 18a and 18b.
In order to provide a complete barrier, the top plate 28 cooperates
with the meter mounting device or an alternative bottom structure
that encloses the voltage and current sensing means 15 from the
side and bottom. FIG. 1a shows an exemplary bottom structure 100
that may be used to cooperate with the top plate 28 of FIG. 1 to
enclose the voltage and current sensing means 15. FIG. 2, discussed
below describes an exemplary meter mounting device that may be used
to cooperate with the top plate 28 to enclose the voltage and
current sensing means 15.
In yet another alternative embodiment, the top plate 28 may be
integral with a side structure or side and bottom structure that
completely encases the voltage and current sensing means 15.
Referring again to FIG. 1, the sockets 30a through 30g and their
corresponding openings are preferably configured to prevent a human
operator from physically contacting the electrically conductive
portions of the socket. In particular, the openings defined by the
sockets 30a through 30g have sufficiently diminutive proportions to
prevent contact of a standard test finger with the electrically
conductive portions of the sockets 30a through 30g. A standard test
finger is a mechanical device used in the electrical industry to
determine whether an electrical connection socket is safe from
accidental contact by a human finger. One standard test finger is
described in Underwriter's Laboratory, Inc., Standard For Safety of
Information Technology Equipment Including Electrical Equipment
Business UL-1950 (Feb. 26, 1993).
In the present embodiment, the openings defined by the sockets 30a
through 30g preferably have a first dimension, for example, the
length, and a second dimension, for example, the width, wherein the
first dimension has at least the same size as the second dimension,
and the second dimension is less than 1/8 inch, thereby preventing
substantial access of a human operator through the openings.
The measurement module 14 comprises a face cover 32, a printed
circuit board 34, and a gasket 36. The printed circuit board 34
includes a display 38, and a measurement circuit FIG. 4, discussed
further below, shows a schematic diagram of a measurement circuit
42 that may readily be used as the measurement circuit on the
printed circuit board 34 of FIG. 1. The measurement circuit is
operable to receive measurement signals and generate energy
consumption data therefrom. The measurement circuit is operably
connected to provide the energy consumption data to the display
38.
The measurement module 14 further includes second interconnecting
means operable to cooperate with first interconnecting means (on
the sensor module 12) to connect the measurement circuit of the
printed circuit board 34 to the voltage and current sensing means
15. For example, in the present embodiment, the measurement module
14 includes a plurality of plugs 40a through 40g that are received
by the corresponding plurality of sockets 30a through 30g. The
plurality of plugs 40a through 40g, when assembled, are
electrically connected to the measurement circuit as described
further below in connection with FIG. 4, and physically connected
to the printed circuit board 34.
FIG. 2 shows an installation configuration that includes the meter
10 and a meter box 13 comprising a housing 16 and a cover 18. The
housing 16 is box-like in structure having an opening for receiving
the cover 18 and a cabling opening 24 for receiving the power lines
of the electrical system being metered, not shown. It will be
appreciated that the housing 16 need not be box-like in structure,
and that any other suitable shape may be used, as long as there is
an opening for receiving a cooperating meter box cover and a
cabling opening. The housing 16 further includes an interior 20.
Within the interior 20 are located a plurality of jaws 22
constructed of electrically conductive material. When installed
into a facility, the plurality of jaws 22 are electrically
connected to the power lines of the electrical system of the
facility, not shown.
The plurality of jaws 22 receive and provide electrical connection
to the current coil blades 22a, 24a, 22b and 24b (see FIG. 1) as
well as the neutral blade or blades 20. The relationship of the
jaws and the blades 22a, 24a, 22b, and 24b also define the
alignment of the sensor module 12 within the housing 16. Once the
blades 22a, 24a, 22b, and 24b (see FIG. 1) are engaged with the
plurality of jaws 22 (FIG. 2), then the sensor module 12 is
installed within the interior 20 of the housing 16. The cover 18 is
then installed onto the housing 16. The cover 18 includes a meter
opening 25 having a perimeter defined by the perimeter of the
sensor module 12. Preferably, the perimeter of the meter opening 25
has substantially the same shape and is slightly smaller than the
perimeter of the sensor module 12 such that the sensor module 12
cannot be removed when the cover 18 is engaged with the housing
16.
Once the cover 18 is installed, the measurement module 14 in the
present embodiment is placed in engagement with the sensor module
12 through the meter opening 25 of the meter box cover 18. When in
engagement, the plugs 40a through 40g of the measurement module 14
are electrically connected to the sockets 30a through 30g,
respectively, of the sensor module 12. (See FIG. 1). Once the
measurement module 14, cover 18, sensor module 12 and housing 16
are all assembled as described above, the meter 10 (i.e., sensor
module 12 and measurement module 14) performs energy consumption
measurements on the electrical system of the facility.
The configuration of the meter box 13 in FIG. 2 is a standard
mounting device known as a ringless-type mounting device. It will
be noted that the meter 10 may readily be adapted for use in a
ring-type mounting device. A ring-type mounting device differs from
the meter box 13 in FIG. 2 in that the sensor module 12 would be
installed after the meter box cover 18 is assembled onto the
housing 16. An annular ring would then be used to secure the sensor
module 12 to the meter box cover 18. To this end, the standard
meter box cover for use in a ring type mounting device includes a
feature annularly disposed around the opening 25 that cooperates
with the annular ring to engage and secure the sensor 12
thereto.
FIG. 3 shows a schematic circuit diagram of the sensor module 12 of
the exemplary embodiment shown in FIG. 1. According to the present
embodiment, the sockets 30a and 30b provide a connection to the
first current transformer 16a, the sockets 30e and 30f provide a
connection to the second current transformer 16b, the socket 30c
provides a connection to the first current coil 18a, the socket 30d
provides a connection to the second current coil 18b, and the
socket 30g provides a connection to one or more of the neutral
blades 20.
Further detail regarding the physical configuration of the sockets
30a through 30g, as well as the configuration of the top plate 28
is discussed further below in connection with FIG. 5.
FIG. 4 shows an exemplary measurement circuit 42 and associated
display 38 for use on the printed circuit board 34 in the
measurement module 14 of FIG. 1. The measurement circuit 42
includes a first watt measurement integrated circuit ("IC") 44, a
second watt measurement IC 46, a microprocessor 48 and a
non-volatile memory 50. Plugs 40a, 40b, and 40c are each connected
to the first watt measurement IC 44. The first watt measurement IC
44 is a device that receives measurement signals representative of
voltage and current signals in an electrical system, and generates
an energy pulse signal and a polarity pulse signal therefrom. The
energy pulse signal is a stream of pulses wherein the frequency of
the pulses is proportional to watt-hours measured. The polarity
pulse signal contains information relating to the polarity of the
phase A measurement signal. The first watt measurement IC 44 is
operable connected to provide energy pulse signals and polarity
pulse signals to the microprocessor 48. Circuits suitable for
carrying out the functions of the first watt measurement IC 44 are
well known.
Plugs 40d, 40e, and 40f are connected to the second watt
measurement IC 46. The second watt measurement is device
substantially similar to the first watt measurement IC 44. The
second watt measurement IC 46 is operable connected to provide
energy pulse signals and polarity pulse signals to the
microprocessor 48. The microprocessor 48 is further connected to
the memory 50 and the display 38.
In the operation of the exemplary meter 10 and meter box
configuration described above in connection with FIGS. 1, 2, 3, and
4, energy consumption measurements are carried out in the following
manner. As discussed above, the present embodiment is intended for
use with a 12S meter form that is generally associated with a three
wire network configuration. A three wire network configuration, as
is well known in the art, includes a phase A power line, a phase C
power line, and a neutral line. The present invention, however, is
in no way limited to use in a three wire network configuration. The
concepts described may readily be employed in meters used in other
configurations, including single phase and other polyphase
configurations.
In operation, the plurality of jaws 22 (FIG. 2) provide the phase A
power line signal, in other words, the phase A voltage and current,
across the blades 22a and 24a of the first current coil 18a, and
the phase C power line signal across the blades 22b and 24b of the
second current coil 18b. (FIG. 1). Referring to FIG. 3, the phase A
current flows from the blade 24a through the first current coil 18a
to the blade 22a. The first current coil 18a imparts a scaled
version of the current, referred herein as the phase A current
measurement signal, to the first current transformer 16a. The phase
A current measurement signal is equal to the current flowing
through the current coil 18a scaled by a factor of N1, where N1 is
the turns ratio of the current transformer 16a. The phase A current
measurement signal is provided to the sockets 30a and 30b. The
first current coil 18a is further operably connected to the socket
30c for the purposes of providing the phase A voltage thereto.
Similar to the phase A current, the phase C current flows from the
blade 24b of the second current coil 18b to the blade 22b. The
phase C current is imposed onto the second current transformer 16b,
which generates a phase C current measurement signal. Analogous to
the phase A current measurement signal, the phase C current
measurement signal is the phase C current scaled by a factor of N2,
where N2 is the turns ratio of the second current transformer 16b.
The turns ratios N1 and N2 of the current transformers 16a and 16b,
respectively, are typically substantially similar and preferably
equal. However, manufacturing tolerances may result in slight
differences in the turns ratios N1 and N2. In any event, the second
current transformer 16b provides the phase C current measurement
signal to the sockets 30e and 30f. The second current coil 18b is
operably connected to the socket 30d for the purposes of providing
the phase C voltage thereto. The neutral blade 20 is connected to
provide a connection between the neutral line and the socket
30g.
It is noted that potentially hazardous electrical signals reside on
one or more of the sockets 30a through 30g. In particular, the
sockets 30c and 30d provide a direct connection to the external or
utility power line, and therefore are potentially extremely
dangerous. Moreover, the sockets 30a, 30b, 30e, and 30f all include
current measurement signals that are potentially dangerous to
humans, depending somewhat on the overall power consumption of the
facility being metered and the turns ratios N1 and N2. Accordingly,
the relatively small physical size of the sockets 30a through 30g
and their corresponding openings greatly inhibits or prevents human
contact with the socket connections.
Continuing with the general operation of the meter 10 of FIG. 1,
the sockets 30a and 30b (FIG. 3) provide the phase A current
measurement signal to the plugs 40a and 40b, respectively, of the
measurement module (FIG. 4). Likewise, the sockets 30e and 30f
(FIG. 3) provide the phase C current measurement signal to the
plugs 40e and 40f, respectively of the measurement module (FIG. 4).
The sockets 30c and 30d (FIG. 3) provide, respectively, the phase A
voltage measurement signal and the phase C voltage measurement
signal to the plugs 40c and 40d (FIG. 4). The neutral plug 30g
(FIG. 3) is operably connected to the plug 40g of FIG. 4.
Referring to FIG. 4, plugs 40a and 40b provide the phase A current
measurement signal to the first watt measurement IC 44. Preferably,
a shunt resistor RSHA is connected across the plugs 40a and 40b in
order to convert the phase A measurement signal into a voltage
signal having a magnitude and phase that is representative of the
measured phase A current. The converter phase A current measurement
signal is provided to the first watt measurement IC 44. The socket
40c provides the phase A voltage measurement signal through a
voltage divider network VDNA to the first watt measurement IC 44.
The voltage divider network VDNA reduces the magnitude or, in other
words, scales down of the phase A voltage magnitude signal before
it is input to the first watt measurement IC 44. It is noted that
the voltage divider network VDNA may alternatively be located in
the sensor module 12, as opposed to the measurement module 14.
The sockets 40e and 40f, analogous to the sockets 40a and 40b,
provide the phase C current measurement signal through a shunt
resistor RSHC to the second watt measurement IC 46. The socket 40d
provides the phase C voltage measurement signal through a voltage
divider network VDNC to the second watt measurement circuit 46. The
socket 40d further provides the phase C voltage measurement signal
to the power supply 60. The power supply 60 is further connected to
the neutral line and operates to provide a biasing voltage to each
of the functional block circuits in the measurement module 14.
The first watt measurement IC 44 receives the phase A voltage and
current measurement signals, or simply, phase A measurement
signals, and generates a phase A energy pulse signal therefrom. To
this end, the first watt measurement IC 44 may suitably include an
analog to digital ("A/D") converter and a digital signal processing
circuit. In such configuration, the A/D converter would sample the
phase A measurement signals and provide the digitized phase A
measurement signals to the digital signal processing circuit. The
digital signal processing circuit would then multiply each phase A
voltage measurement sample by each phase A current measurement
sample, and accumulate the resulting products over time to obtain
an energy measurement in watt-hours. When enough watt-hours
accumulate, or in other words, when the accumulated watt-hour
measurement exceeds a predetermined threshold, or pulse threshold,
the digital signal processing circuit generates a pulse as an
output, thereby creating the phase A energy pulse signal. The
accumulated watt-hour measurement is then reset to zero. The first
watt measurement IC 44 provides the phase A pulse energy signal to
the process 48.
The frequency of the pulses in the phase A energy pulse signal is
proportional to the amount of energy being consumed. For example,
if a relatively large amount of energy is being consumed, then the
phase A current measurement signal will have a relatively large
magnitude. As a result of such a large current measurement signal,
the products of the current and voltage sample multiplication will
be relatively large, thereby causing the pulse threshold to be
reached in a shorter amount of time. Accordingly, when a large
amount of energy is being consumed, the first watt measurement IC
44 will generate pulses more quickly, or in other words, at a
higher frequency.
The first watt measurement IC 44 further generates a phase A energy
polarity signal. The phase A energy polarity signal consists of the
sign of the average valve of the product of the phase A voltage
measurement signal and the phase A current measurement signal.
The second watt measurement IC 46 operates in a substantially
similar manner as the first watt measurement IC 44. Specifically,
the second watt measurement IC 46 receives the phase C voltage and
current measurement signals, or simply, phase C measurement
signals, and generates a phase C energy pulse signal and a phase C
energy polarity signal therefrom. To this end, the second watt
measurement IC 46 may suitably be constructed and operate in
substantially the same manner as the first watt measurement IC
44.
It will be appreciated that the above descriptions of the operation
of the first and second watt measurement ICs 44 and 46,
respectively are given by way of example only. Other methods of
energy measurement using voltage and current measurement signals
are well known and may readily be incorporated to suit the needs of
the particular metering application. For example, a single watt
measurement IC may be used for both phase A and phase C.
Additionally, the watt measurement circuit need not be integrated
into a single semiconductor substrate but instead may comprise
discrete components. Those of ordinary skill in the art may readily
devise their own watt measurement circuit to suit their particular
design criteria.
The processor 48 then accumulates the energy pulses from the energy
pulse signal to obtain measurement data of energy consumed by the
facility to which the meter 10 is connected. The measurement data
may then be provided to the display 38.
It is noted that in the exemplary embodiment described herein, the
meter 10 is a type of meter commonly known in the industry as a
self-contained meter. In a self-contained meter, the current coils
of the meter, such as current coils 18a and 18b of the present
invention, carry the entire current load of the electrical system.
As a result, in a typical meter, if the meter is removed for repair
or replacement, the current coils are removed from the jaws of the
meter box, and power to the facility is interrupted. A distinct
advantage of the present invention is that the measurement module
14 may be removed for repair, replacement or upgrade without
removing the current coils 18a and 18b. As a result, the facility
experiences no electrical service interruption during the
replacement.
FIG. 5 shows a side view cutaway of the meter 10 wherein the
measurement module 14 is assembled onto the sensor module 12. The
face cover 32 of the measurement module 14 includes a cylindrical
portion 62 and an annular skirt 64. The top plate 28 of the sensor
module 12 is defined in part by an annular ridge 66. The annular
ridge 66 is received by a space defined in between the annular
skirt 64 and the cylindrical portion 62 of the meter cover 32. The
top plate 28 is further defined by a shelf 68 that is substantially
flat and abuts, in part, the cylindrical portion 62. The shelf 68
constitutes approximately one-half of the top plate 28. The other
half of the top plate 28 consists of a depression 56 defined by a
drop 70, a bottom 72 and a portion of the annular ridge 66. The
drop 70 defines the change in depth between the shelf 68 and the
bottom 72.
The depression 56 defines a space that allows for large components
on the printed circuit board 34 to extend downward from the
measurement module 14 below the cylindrical portion 62. In the
illustrated example, components of the power supply 60 extend below
the cylindrical portion 62 to occupy at least a portion of the
depression 56. The two level configuration of the top plate created
by the depression 56 of the sensor module 12 more efficiently
utilizes the space within the meter 10. By contrast, prior art
modular meters included a substantially flat interface between the
sensor module and electronics module, which creates wasted space in
both modules. The present invention, by arranging for the bulky
components to occupy complementary portions of the meter and using
an interface that includes a depression, space within the meter is
more efficiently utilized.
As illustrated in FIGS. 1 and 5, the current transformer 16b is
arranged to be horizontally disposed, or in other words, has an
axial dimension that is parallel to the axial dimension of the face
cover 32. As illustrated in FIG. 1, the first current transformer
16a is similarly disposed. The horizontally disposed current
transformers 16a and 16b provide significant space reduction
advantages over vertically-disposed current transformers. In an
electric utility meter, the horizontal footprint, for example, the
length and width or diameter, is defined predominantly by the meter
mounting equipment. For example, the plurality of jaws 22 of FIG. 2
define at least a minimum length and width, or in this case using a
circular meter shape, a minimum diameter. The meter box, such as
the meter box 15 of FIG. 2 may also dictate the minimum diameter.
Accordingly, the only space reduction that is practical is in the
thickness or depth dimension. By disposing the current transformer
16b horizontally, the smallest dimension of the current transformer
16b, its axial thickness, is aligned in the only dimension of the
meter that can be reduced. Accordingly, the horizontally-disposed
current transformers 16a and 16b further reduce the overall size of
the meter 10.
As discussed above the top plate 28 also includes a plurality of
openings, illustrated in FIG. 5 by the exemplary opening 52d. The
opening 52d corresponds to the socket 30d, and similar openings
exist that correspond to each of the other sockets 30a, 30b, 30c,
30e, 30f and 30g. (See FIG. 1) The opening 52d is preferably
slightly conical to allow for alignment adjustment of the plug 40d
during assembly of the measurement module 14 onto the sensor module
12. The socket 30d, which may suitably be a spring loaded terminal,
is electrically connected to the current coil 18b for the purposes
of providing a connection to the phase C voltage measurement, as
discussed above in connection with FIG. 1.
FIG. 5 further shows the plug 40d connected to the circuit board 34
and inserted through the opening 52d and into the socket 30d. The
socket 30d physically engages the plug 40d in such a manner as to
provide an electrical connection therebetween. The plug 40d may
suitably be an ordinary conductive pin.
It can thus be seen by reference to FIGS. 1, 2 and 5, that the
electrically safe interface or top plate 28, when fitted to a
cooperating meter housing, provides a substantially solid barrier
between a human operator or technician and the current and voltage
sensing devices when the measurement module 14 is removed for
repair or replacement. The only openings are the openings, for
example, opening 52d, that correspond to the sockets 30a through
30g to permit the plugs 40a through 40g to connect to the sockets
30a through 30g. Such openings are sufficiently small enough, and
the sockets are sufficiently recessed within the openings, to
prevent an operator from coming into direct contact with dangerous
high voltages.
It will be appreciated that other interconnection means may be
employed in the sensor module 12 and measurement module 14 that
will nevertheless provide an electrically safe interface. For
example, wireless means may be used as the interconnection means.
Such wireless means could provide voltage and current measurement
signals from the sensor module 12 to the measurement module 14. For
example, the measurement module 14 could include sensitive electric
and magnetic field sensors that obtain voltage and current
measurement information from electromagnetic radiations from the
current coils 18a and 18b. Likewise, optical communication means
may be used to provide measurement signal information from the
sensor module 12 to the measurement module. In any case, the
electrically safe interface would typically include a barrier such
as the top plate 28 that prevents physical access by a human
operator to the current coils 18a and 18b and other dangerous
portions of the sensor module 12 when the measurement module 14 is
removed.
To fully obtain the benefits of modularity, it is necessary to
address calibration issues in the design of the meter 10.
Specifically, the sensor portion 12 of the meter must have a
calibration feature that allows it to be used in connection with
any suitable measurement portion. In non-modular meters, the
measurement circuit is often specifically calibrated for use with a
particular voltage and current sensing means. The reason for the
specific calibration is that there can be large variations in
signal response of each voltage and current sensing means. In
particular, the current sensing devices, such as current
transformers, often have a widely variable signal response. The
signal response of commonly available current transformers varies
widely in both magnitude and phase response.
The signal response of such current transformers varies to a much
greater extent than the energy measurement accuracy of the meter.
In other words, while the current transformer signal response may
vary as much as 10%, the overall accuracy of the meter is required
to be much less than 10%. Accordingly, compensation must be made
for the variance, or tolerance, of the current sensing devices to
ensure that the ultimate energy measurement accuracy of the meter
is within acceptable tolerances. The compensation is typically
carried out in the prior art by adjusting or calibrating the
measurement circuit during manufacture to account for the signal
response characteristics of the current sensing devices that will
be used in a particular meter unit. In other words, each
measurement circuit is custom-calibrated for each meter.
A truly modular meter, however, cannot require such extensive
unit-specific calibration. Instead, the modular components must be
readily interchangeable. Accordingly, referring again to FIG. 1,
the sensor module 12 is pre-calibrated for modularity, such that
the sensor module 12 may be coupled with any measurement module 14
without requiring unit-specific calibration of that measurement
module 14.
To this end, the sensor module 12, and specifically the voltage and
current sensing means 15 is pre-calibrated such that the voltage
and current sensing means has a signal response within a tolerance
of a predefined signal response that is no greater than the
tolerance of the energy measurement accuracy of the meter 10. The
energy measurement accuracy of the meter 10 is defined as the
accuracy of the measured energy consumption with respect to the
actual energy consumption of the facility. Thus, if the tolerance
of the energy measurement accuracy of the meter is required to be
0.5%, then the difference between the measured energy consumption
and the actual energy consumption will not exceed 0.5%. In such a
case the tolerance of the signal response of the voltage and
current sensing means will be no more than, and typically
substantially less than, 0.5%. As a result, the measurement module
14 may readily be replaced with another measurement module without
requiring specific calibration of the replacement measurement
module.
The pre-calibration of the voltage and current sensing means 15 may
be accomplished using careful manufacturing processes. The primary
source of variance in the signal response of the voltage and
current sensing means 15 is the signal response of the current
transformers 16a and 16b. Generally available current transformers
are prone to variance in both magnitude and phase angle signal
response. Accordingly, pre-calibration involves using current
transformers that are manufactured to perform within the required
tolerances. As an initial matter, the current transformers 16a and
16b are manufactured using a high permeability core material, which
reduces phase angle variance in the signal response. More over, the
current transformers 16a and 16b are manufactured such that the
actual number of turns is closely controlled. Close manufacturing
control over the number of turns in the current transformers 16a
and 16b produces sufficient consistency in the magnitude signal
response to allow for interchangeability.
Alternatively, if controlling the number of turns during initial
manufacturing is not desirable for cost reasons, then turns may be
added or removed after manufacturing to achieve the desired signal
response. For example, it may be more cost effective to buy wide
tolerance commercially available current transformers and adjust
the number of turns than to have sufficiently narrow tolerance
current transformers specially manufactured.
In any event, the meter 10 described above in connection with FIGS.
1 through 5 provides features and advantages to servicing,
upgrading, and repairing revenue meters. Accordingly, the present
invention includes method of servicing an electronic utility meter
in a manner that does not interrupt the electrical service to the
facility being metered.
Referring to FIG. 2, the servicing method described herebelow
involves servicing the meter 10, which is installed in the meter
box 15, which in turn is attached to the electrical system of the
facility being metered, not shown. The types of servicing that may
be accomplished by the following method include replacement of the
measurement module 14, repair of the measurement module 14, and
upgrading of the measurement module 14. Because the components of
the measurement module 14 have higher complexity, a large
proportion of the repair, replacement, and upgrade activity that is
potentially possible with respect to the meter 10 will involve only
the measurement module.
Typically, a technician first removes the measurement module 14 of
the electronic utility meter 10 from the sensor module 12 while the
cover 18 remains installed over the sensor module 12 and onto the
housing 16. The measurement module 14 operates having a first level
of performance which requires replacement, repair, or upgrading, to
a second level of performance. When the measurement module 14 is
removed, the sensor module 12 remains electrically connected to the
electrical system of the facility, thereby allowing electrical
power to be delivered to the facility.
The technician then replaces the measurement module 14 with a
replacement measurement module having a second level of
performance. The replacement measurement module may suitably be the
same measurement module 14 wherein the technician has performed
operations, such as repair, upgrade, or component replacement, to
create the replacement module having the second level of
performance.
An exemplary upgrade operation includes upgrading the measurement
circuit 42 (see FIG. 4) to add features or capabilities. Revenue
meters are often capable of sophisticated self-diagnostics, demand
metering, time-of-use metering, and communication functionalities.
Sometimes, the owner of the facility being metered, or the utility
providing the electrical power, desires to improve the capabilities
of an existing meter. The capabilities may be improved by upgrading
the measurement circuit 42. In such a case, the first level of
performance defines the original performance capabilities and the
second level of performance includes additional capabilities.
An exemplary repair operation may include the replacement of
components. At times, one or more components of the measurement
module 14 will fail, in which case, the first level of performance
may be an inoperative level of performance. In such a case, the
method described above further comprises performing an operation
including replacing the at least one inoperative component to
create the replacement module having a second level of
performance.
In yet another exemplary operation, the above method may include
replacing the measurement module 14 with an entirely different
measurement module. If the measurement module 14 requires repair or
upgrade, it is often desirable to simply replace the measurement
module 14 having the first level of performance with another
measurement module that has the second level of performance.
In any of the above described servicing scenarios, the power to the
facility need not be interrupted. This provides a significant
advantage over prior art methods of servicing meters that required
a power service over prior art methods of servicing meters that
required a power service interruption to repair or replace meter
components. The above method is not limited to use in connection
with the exemplary embodiment described above, but is suitable for
use in connection with any modular meter that includes an
electrically safe interface between the module to be removed, for
example, the measurement module, and the module that is not
removed, for example, the sensor module.
It will be understood that the above embodiments are merely
exemplary, and that those of ordinary skill in the art may readily
devise their own implementations that incorporate the principles of
the present invention and fall within the spirit and scope thereof.
For example, while the meter 10 includes a display 38, other means
for communicating energy consumption data may alternatively be
employed, such as serial or parallel communication lines to an
external computer or module, on-board printing devices, and audible
communication devices.
Moreover, the present invention is in no way limited to meters that
utilize current transformers and current coils as voltage and
current sensing means. The principles and advantages of the present
invention are readily incorporated into meters utilizing voltage
and current sensing means that include current shunt sensing
devices, inductive current pickup devices, Hall-effect current
sensors, and other well-known voltage and current sensing
devices.
* * * * *